THE  RELATION  OF  EXGESS  BLEACH, 
TEMPERATURE,  AND  CONSISTENCY 
TO  THE  LOSS  OF  STRENGTH  AND 
SHRINKAGE  OF  WOOD  PULP 
ON  BLEACHING 


SIDNEY  PERCY  FOSTER 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 


CHEMICAL  ENGINEERING 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 


UNIVERSITY  OF  ILLINOIS 


1922 


Digitized  by  the  Internet  Archive 

in  2016 


https://archive.org/details/relationofexcessOOfost 


192  2 
FBI 


UNIVERSITY  OF  ILLINOIS 


May  ?0 


.19^2 


THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 


S.ydne_Y_  P . __F os  ter 

ENTITLED delation  of  Excess  Bleach,  Temperature,  and  Consist- 

ing. 

encv  To  The  Loss  of  Strength  and  Shrinkage  of  wood  Pulp  On  Pleach- 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 


DEGREE  OF  __Bac_hejLoj^ _^f  _ScJLer^ce 

in 

C h e m i c a 1_  _ E n_gi  ne  er _i  n_g_. 


Instructor  in  Charge 


Approved 


HEAD  OF  DEPARTMENT  OF 


500 1 8? 


ACKNOWLEDGEMENT 

The  author  desires  to  express  his  appreciation  to  Dr.  D.  T. 
Englis,  under  whose  direction  this  research  was  carried  out, 
in  appreciation  of  his  excellent  advice,  kindly  encouragement, 
and  many  favors  throughout  the  course  of  this  work,  and  also  to 
Lewis  Armstrong  of  the  Kimberly  Clark  Paper  Mills  Co.,  Niagara, 
Wis.,  for  many  suggestions,  favors,  and  help. 


TABLE  OF  CONTENTS 


Introduction  1 

Object  of  the  Investigation . 1 

Nature  of  Wood  Pulp • • 1 

Manufacture  of  Wood  Pulp  2 

Bleaching  of  Wood  Pulp 5 

Experimental  Part 7 

Procedure . 7 

Description  of  Apparatus  10 

Preparation  of  Materials  10 

Results 11 

Discussion  and  Conclusion 15 

Summary 17 

Bibliography  18 


1 


INTRODUCTION 

Object  of  the  Investigation,  The  object  of  this  investi- 
gation was  to  determine  the  relation  of  excess  bleach,  tempera- 
ture, and  consistancy  to  the  loss  of  strength  and  shrinkage  of 
wood  pulp  on  bleaching.  It  is  logical  to  expect  that  the  strength 
and  shrinkage  of  pulp  on  bleaching  will  vary  inversely  as  the 
temperature  and  the  percent  excess  bleach.  In  other  words, 
the  higher  the  temperature,  and  the  greater  the  excess  bleach, 
the  greater  will  be  the  loss  in  the  strength  and  weight  of  the 
pulp.  However,  the  problem  here  was  to  determine  the  quanti- 
tative relation  of  these  factors  and,  if  possible,  to  get  the 
necessary  data  required  to  state  exactly  what  the  optimum  temp- 
erature and  percent  excess  bleach  would  be  for  a minimum  loss  in 
strength  and  shrinkage  of  pulp. 

No  doubt  much  work  has  been  done  on  this  subject,  but  only 
in  a disjointed  way  insofar  as  literature  is  concerned.  Ap- 
parently there  has  never  been  anything  published  that  covers 
the  work  completely.  Much  of  the  knowledge  of  this  phase  of 
paper  manufacture  is  in  the  form  of  plant  secrets  and,  conse- 
quently, very  little  is  to  be  found  about  it  in  the  literature. 

Nature  of  Wood  Pulp.  A brief  statement  of  a few  facts 
about  wood  pulp  and  the  processes  and  problems  involved  in  its 
bleaching  may  be  helpful  in  giving  a clearer  conception  of  what 
is  to  follow. 

Wood  pulp  is  a product  coming  almost  entirely  from  soft 
woods.  It  consists  mainly  of  cellulose  associated  with  a 
smaller  amount  of  lignin  occurring  in  the  raw  fibers.  This 


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lignin  associated  with  the  cellulose  carries  with  it  certain 
colored  bodies  of  complex  composition  that  give  the  wood  pulp  a 
brownish  color.  Wood  pulp,  if  it  is  to  be  used  for  making  any 
light  colored  papers,  must,  therefore,  be  bleached,  as  these 
colored  impurities  cannot  be  removed  by  any  amount  of  washing 
or  other  mechanical  treatment.  It  is  believed  that  they  are 
combined  in  a chemical  manner  with  the  fiber  or  cellulose  and, 
therefore,  a chemical  process  is  necessary  for  their  removal. 

In  addition  to  these  colored  impurities  which  are  ordinarily 
present  in  the  pulp,  other  dark  colored  substances  are  produced 
during  the  process  of  manufacturing  the  pulp.  The  production 
of  these  coloring  substances  is  due  to  the  chemical  action  of 
the  qcidic  or  alkaline  solutions  used  in  the  sulphite  and  soda 
processes  respectively. 

Manufacture  of  Wood  Pulp.  A brieifi  outline  of  the  processes 
of  chemical  wood  pulp  manufacture  may  help  to  make  this  distin- 
ction clear. 

Most  vegetable  fibers  are  converted  into  pulp  by  alkaline 
processes,  that  is,  by  digesting  the  raw  materials  with  caustic 
soda  and  similar  alkaline  substances.  Wood  may  be  treated  in 
one  of  two  ways,  one  of  which  is  the  ordinary  soda  process,  and 
the  other  an  acid  treatment  requiring  the  use  of  sulphurous  acid. 

For  preparation  of  the  wood  to  be  used,  the  logs  are  cut  up 
and  then  "flaked"  into  pieces  one  inch  square,  and  one-half  inch 
thick  by  means  of  chippers.  To  insure  uniformity  in  size,  the 
chips  are  sifted  on  wire  cloth. 

The  chips  are  then  put  into  digesters.  The  digesters  are 
either  spherical,  cylindrical,  or  egg-shaped,  being  constructed 


3 

to  revolve  at  a slow  rate  of  speed,  or  fixed  permanently  in  an 
upright  position.  The  object  of  boiling  the  wood  under  pressure 
with  chemicals  in  the  digesters  is  to  dissociate  the  valuable 
fibrous  portion  of  the  plant  from  the  resinous  and  non-fibrous 
portion.  The  contents  of  the  digester  are  heated  by  means  of 
high  pressure  steam,  which  is  blown  directly  into  the  mass  or 
passed  through  a coil  lying  at  the  bottom  of  the  vessel. 

Sulphite  Wood  Pulp.  This  name  is  given  to  pulp  prepared 
by  digesting  wood  with  solutions  containing  sulphurous  acid, 
or  salt  of  the  acid  (bisulphate  of  lime). 

The  digesters  are  charged  with  the  chipped  wood  and  the  re- 
quisite amount  of  sulphite  liquor  is  added.  Some  digesters  are 
capable  of  holding  20  tons  of  wood  at  one  charge.  The  length 
of  time  of  cooking  varies  Jh»om  7 hours  to  60  hours  depending  on 
the  kind  of  wood,  size  of  charge,  ultimate  product  desired, 
and  the  yield.  No  hard  and  fast  rule  for  cooking  can  be  given 
and  each  mill  has  its  own  particular  method.  80  pounds  pressure 
is  usually  employed. 

When  the  wood  has  been  sufficiently  boiled,  the  spent  sulphite 
liquor  is  drained  from  the  digester.  The  wood  is  then  washed 
well  with  water  to  remove  all  residual  liquors. 

The  woody  mass  is  next  screened.  Here  all  the  knots, 
large  pieces  of  unsoftened  wood,  and  coarse  pieces  are  removed. 
From  the  screens,  the  mixture  of  pulp  and  water  is  pumped  into 
a concentrator.  Here  some  of  the  water  is  removed.  The  mass 
of  wet  pulp  is  then  conveyed  into  a circular  reservoir  or  “stuff 
chest"  which  serves  to  supply  the  machines  used  for  converting 
the  pulp  into  dry  sheets.  The  pulp  flows  in  a continuous 


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stream  on  to  a horizontal  endless  wire,  which  carries  it  forward 
as  a thin  layer;  the  water  drains  through  the  meshes  of  the  wire, 
further  quantities  being  removed  by  "suction  boxes".  The  wet 
sheet  then  passes  between  "couch  rolls"  which  compress  the  pulp, 
and  then  through  press  rolls  which  finally  give  a firm  adherent 
sheet  of  pulp  containing  70  percent  of  water.  The  sheet  is 
then  dried  by  passing  over  a number  of  steam  heated  cylinders. 

Soda  Wood  Pulp.  The  chipped  wood  is  boiled  in  digesters  at 
a pressure  of  70--80  lbs.  A solution  of  caustic  soda  is  em- 
ployed, about  16 — 20  percent  of  the  weight  of  the  wood  being 
added  to  the  contents  of  the  digester.  Live  steam  is  blown 
direct  into  the  mass,  and  after  the  operation,  the  spent  liquor 
is  kept  for  subsequent  treatment.  After  digestion,  the  pulp 
is  washed  in  such  a manner  that  the  amount  of  water  actually  used 
is  kept  down  to  the  smallest  possible  volume  consistent  with  the 
complete  removal  of  soluble  matters.  This  is  done  in  order  that 
the  spent  liquors  may  be  treated  for  the  recovery  of  the  soda. 
From  here,  the  v/ood  pulp  is  screened,  rolled,  and  dried  as  in  the 
sulphite  process. 

Two  other  processes  for  making  wood-pulp  are  the  sulphate 
process  and  the  Mitscherlich  process.  The  former  consists  of 
digesting  the  wood  with  a mixture  of  caustic  soda,  sulphide  of 
soda,  and  sulphate  of  soda.  The  latter  process  consists  of  di- 
gesting the  wood  with  bisulphite  of  lime  at  a much  lower  temper- 
ature, and  for  a longer  period  than  the  ordinary  sulphite  pro- 
cess. 

It  is  these  acidic  and  alkaline  solutions  employed  in  the 
different  processes  that  react  with  some  constituents  in  the  wood 


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pulp  to  produce  colored  complexities  that  have  to  be  bleached 
out. 

Bleaching  of  Wood  Pulp.  The  object  of  all  successful  bleach- 
ing is  to  thoroughly  bleach  the  pulp  ao  as  to  produce  a product 
of  maximum  whiteness  and  purity,  which  will  remain  white  inde- 
finitely, and  at  the  samfe  time  not  impair  the  strength  and 
natural  properties  of  the  fiber,  and  not  to  cause  too  great  a 
shrinkage  in  weight  and  volume. 

The  process  of  bleaching  is  essentially  one  of  oxidation 
and  the  success  attained  depends  on  the  fact  that  the  impurities 
are  attacked  and  resolved  into  soluble  products  much  more  easily 
than  the  comparitively  inert  cellulose  of  which  the  impure  fiber 
is  largely  composed.  Many  different  oxidizing  agents  can  be 
utilized  in  the  bleaching  process  and  a number  of  them  have  been 
applied  with  more  or  less  success.  Practically  all  commercial 
work  is  performed  by  chlorine,  or  some  of  its  compounds* 

Some  of  the  bleaching  agents  used  are  chlorine  gas,  hypochlo- 
rites, bleaching  powder,  and  electrolytic  bleach. 

There  are  many  factors  entering  into  the  bleaching  of  wood 
pulp.  Those  upon  which  the  shrinkage  and  loss  in  strength 
depend  are  as  follows: 

1.  The  raw  material  from  which  the  pulp  is  made. 

2.  The  process  employed  in  the  manufacture. 

3.  The  purity  of  the  pulp  obtained. 

4.  The  density  of  the  stock  during  bleaching. 

5.  The  temperature  at  which  the  bleaching  was  carried  out, 

6.  The  time  allowed  for  bleaching. 

7.  The  percent  excess  bleach  used. 


. 

.. 


6 


It  has  been  found  that  the  greater  the  yield  of  fiber  from 
unit  weight  of  raw  material,  no  matter  by  what  process  the  pulp 
has  been  made,  the  greater  is  the  loss  of  weight  of  pulp  bleached 
and  the  amount  of  bleaching  agent  required. 

The  quality  of  water  used  for  cleaning  the  pulp  also  has  an 
influence  on  the  bleaching  factors,  especially  if  the  water  con- 
tains any  lime.  in  the  sulphite  process,  the  lime  salts  pre- 
cipitate insoluble  resin  soaps  on  the  surface  of  the  fibers. 

These  resin  soaps  absorb  chlorine.  A similar  precipitation 
takes  place  when  water  containing  lime  is  used  for  washing  soda 
or  sulphate  pulp.  In  both  of  these  cases,  the  resin  soaps 
formed  cling  to  the  fibers,  and  carry  down  with  them  the  organic 
coloring  matter  in  the  fibers,  thus  rendering  the  bleaching 
process  more  difficult  and  costly. 


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7 

EXPERIMENTAL  PART 

Procedure . The  procedure  followed  in  the  determination  of 
the  relation  between  the  temperature,  excess  bleach,  consistency, 
and  the  loss  of  strength  and  weight  on  bleaching,  was  a series 
of  tests  in  which  the  conditions  of  bleaching  were  varied. 

In  one  test,  the  temperature,  excess  bleach,  and  consistency 
were  all  kept  constant.  In  the  next  test,  the  excess  bleach 
and  consistency  remained  the  same  as  in  the  preceding  one 
while  the  temperature  was  raised  10  degrees.  In  the  next  test, 
the  temperature  was  again  raised  10  degrees. 

The  kind  of  pulp  used  was  called  No.  2 Balsam  Dryer..  For 
each  test,  a 700  gm.  sample  (air  dry)  was  used.  This  amount 
was  taken  so  as  to  be  able  to  run  strength  tests  on  each  sample. 
The  beaters  and  strength  testers  to  be  used  could  not  handle  an 
amount  smaller  than  700  grams. 

The  bleaching  agent  used  was  commercial  bleaching  powder. 

Following  is  the  procedure  in  detail. 

The  pulp  after  first  being  weighed,  was  torn  into  small  pieces 

/ 

and  placed  in  the  container  in  which  it  was  to  be  bleached  and 
about  three-fourths  of  the  total  volume  of  distilled  water  was 
added.  This  was  stirred  mechanically  until  the  pulp  was  tho- 
roughly broken  up.  In  the  meantime,  the  container  and  contents 
were  brought  up  to  temperature  by  means  of  a heating  coil  and 
maintained  at  that  temperature  by  a thermostat.  Then  the 
balance  of  the  water  and  the  required  amount  of  bleach  liquor 
was  added.  At  this  point  after  the  solution  had  been  stirred 
for  about  five  minutes,  a sample  of  the  liquor  was  taken  and 


8 

titrated  with  1.41  h/lO  areenite  to  determine  the  amount  of  chlo- 
rine present  in  grams  per  liter.  This  was  repeated  every  15 
minutes  to  get  the  rate  of  chlorine  absorption.  From  time  to 
time  during  the  bleaching,  the  whiteness  of  the  pulp  was  com- 
pared with  standard  color  plates  so  as  not  to  overbleach,  which 
would  cause  a greater  loss  in  shrinkage  and  strength. 

Vihen  the  pulp  had  been  bleached  white,  as  indicated  by  the 
color  plates,  check  tests  were  made  on  the  chlorine  present  in 
the  solution.  Then  5%  sodium  bisulphite  or  sodium  thiosulphate 
was  added  to  "kill"  the  remaining  bldach.  The  pulp  was  then 
removed  to  a large  Buchner  funnel  where  it  was  thoroughly  dried 
by  suction.  A sample  was  taken  from  the  pad  of  pulp  and  the 
percent  of  moisture  in  it  was  determined.  The  total  weight  of 
the  pad  was  multiplied  by  this  number  to  get  the  bone-dry  weight 
of  the  pad.  To  get  the  air-dry  weight,  the  bone-dry  weight  was 
multiplied  by  1.1. 

The  loss  of  weight  of  the  pulp  is  due  to  the  decomposition 
of  the  cellulose  and  lignin  by  chlorine,  and  is  called  shrinkage. 

Following  is  a complete  plan  of  the  work  contemplated,  all 
of  which  could  not,  however,  be  completed.  The  second  test, 
i.e.  Series  I,  Test  2,  was  the  same  process  repeated  with  the 
same  conditions,  except  that  a 4%  consistency  was  used. 

Series  I.  Test  3. 

Temperature  and  excess  bleach  same.  Consistency  6 %. 

Series  I.  Test  4. 

Temperature  and  excess  bleach  same.  Consistency  Qfi. 


. 


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v- 


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Series  II.  Test  1. 

Same  tests  made  as  in  Series  I,  except  that  the  temperature 
was  kept  at  35°  instead  of  25°.  Consistency  2%. 

Series  II.  Test  2.  Consistency  4%. 

Series  II.  Test  3.  Consistency  6%. 

Series  II.  Test  4.  Consistency  8%. 

Series  III.  Test  1. 

Same  tests  made  as  in  Series  I,  except  that  the  temperature 
was  kept  at  40°,  instead  of  25° • 

Series  III.  Test  2.  Consistency  4%. 

Series  III.  Test  3.  Consistency  6%. 

Series  III.  Test  4.  Consistency  8%. 

Series  IV.  Test  1. 

Same  tests  hut  with  a temperature  of  45°  C.  Consistency  2%. 

Series  IV.  Test  2.  Consistency  4%. 

Series  IV.  Test  3.  Consistency  6%, 

Series  IV.  Test  4.  Consistency  8%. 

Series  V.  Test  1. 

Same  tests  but  with  a temperature  of  50°  C.  Consistency  2%, 

Series  V.  Test  2.  Consistency  4%. 

Series  V.  Test  3.  Consistency  6%. 

Series  V.  Test  4.  Consistency  8%. 

Then  Series  I,  II,  III,  IV,  and  V,  and  Tests  1,  2,  3,  and  4, 
were  repeated  making  the  same  tests  and  observations,  but  raising 

the  excess  bleach  to  25%.  These  series  were  numbered  VI,  VII, 
VIII,  IX,  and  X. 

Series  I,  II,  III,  IV,  V,  Tests  1,  2,  3,  4,  were  again  re- 
peated using  an  excess  bleach  of  50%.  This  series  was  called 


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XI,  XII,  XIII,  XIV,  and  XV. 

Description  of  Apparatus . The  apparatus  consisted  of  a 
20  gallon  jar  placed  inside  of  a large  barrel,  the  latter  being 
filled  with  water  and  acting  as  a thermostat.  The  temperature 
was  maintained  by  means  of  a heating  coil  controlled  by  a mercury 
regulator  and  relay  as  shown  in  the  diagram. 

The  pulp  was  agitated  in  the  jar  by  means  of  a heavy  glass 
rod  with  paddles  attached,  driven  by  a one-sixteenth  horse  power 
motor. 

Two  agitators  placed  on  opposite  sides  of  the  barrel  and  dri- 
ven by  a small  motor  kept  the  temperature  of  the  apparatus  uniform. 

Preparation  of  Materials . For  the  chemical  work,  the  solu- 
tions used  were  N/lO  iodine,  N/lO  sodium  thiosulphate,  1.41  N/lO 
arsenite,  and  bleach  liquor. 

The  first  two  were  prepared  and  standardized  in  the  usual 

way. 

The  arsenious  oxide  required  purification.  This  purifica- 
tion was  carried  out  as  recommended  by  Treadwell  and  Hall  (1). 

The  arsenious  oxide  was  dissolved  in  hot  HC1  (1:3)  and  the  in- 
soluble sulphide  was  filtered  off.  The  solution  was  cooled  and 
the  arsenic  trioxide  allowed  to  crystallize.  The  mother  liquor 
was  poured  off  and  the  remaining  crystals  were  washed  with  water 
and  then  dried.  The  pure  arsenite  was  obtained  by  sublimation 
of  these  crystals. 

For  preparation  of  the  1.41  N/lO  solution,  7.06  grams  of 
the  arsenite  were  dissolved  in  200  cc.  distilled  water  containing 
28.49  grams  of  Na^CO^.  The  solution  was  diluted  to  1 liter. 


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1.41  N/lO  arsenite  is  used  for  the  reason  that  when  5 cc. 
of  the  bleach  liquor  is  Rested,  then  1 cc.  arsenite  is  equal  to 
1 gm.  of  chlorine  per  liter.  Bleach  liquor  is  spoken  of  and 
expressed  in  terms  of  grams  per  liter. 

The  arsenite  was  standardized  against  N/lO  iodine  which  had 
previously  been  standardized  against  sodium  thiosulphate.  The 
latter  was  standardized  with  copper  foil. 

The  bleach  liquor  was  prepared  according  to  the  method  of 
Cary  and  Niuspratl  (2)  from  commercial  bleaching  powder.  The 
solution  was  made  at  a temperature  of  70 — 80°  F.,  the  ratio  of 
bleach  powder  to  the  water  used  being  .5  lbs.  per  gallon.  This 

mixture  was  agitated  in  a jar  for  one  hour  and  then  allowed  to 
stand  until  most  of  the  suspended  material  had  settled.  The 
clear  liquid  was  then  drawn  off  into  a 5 gal.  carboy  and  stored 
in  the  dark  since  light  hastens  the  loss  of  strength  of  a bleach- 
ing solution. 

Results . 

Normality  of  I2  solution  .07351  N 

Normality  of  arsenite  solution  1.4323  N/lO 
1 cc.  1.41  N/lO  arsenite  * 1 gm.  Cl  per  liter. 

Then  1.4323  N/lO  arsenite  ■ 1.015  gm.  Cl.  per  liter. 

The  bleach  liquor  contained  16.90  gm.  Cl  per  liter. 

The  grams  per  liter  of  bleach  liquor  necessary  for  700  grams 
of  pulp  were  determined  by  the  following  method. 

First  of  all,  the  "bleachability"  of  the  pulp  must  be  known. 
Bleachability  is  the  number  of  grams  of  dry  bleach  (35  % avail- 
able Cl)  necessary  for  bleaching  100  grams  of  air-dry  pulp.  An 
average  bleachability  is  figured  at  about  16  %.  That  means  that 


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12 

16  pounds  of  commercial  calcium  hypochlorite  is  necessary  for 
every  hundred  pounds  of  pulp.  Bleaching  powder  is  figured  on 
a 35%  basis.  Then  using  grams  instead  of  pounds,  16  gms. 
bleaching  powder  contain  .35  x 16,  or  5.6  gms.  Cl,  the  amount 
of  Cl.  necessary  for  every  100  gms.  of  pulp.  So  for  700  gms. 
of  pulp,  7 x 5.6  or  39.2  gms.  of  Cl  would  be  required.  To 
determine  the  liters  of  bleach  liquor  necessary  then: 

39^2  gras,  chlorine  required  „ 2.320  liters  (-  % excess) 

1679  gms.  Cl  per  liter  in  liquor 

All  of  these  calculations  may  be  reduced  to  the  following 
formula : 

gl«ac.h?billty  x 700  x .85  x (100  .ft  excess)  , liters  requirec 
100  x gm.  Cl  per  liter  in  liquor 


Rate  of  Chlorine  Absorption  and  Percent  Loss  in  Weight  of  Pulp 


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Due  to  an  error  in  calculations, 
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the  constant,  109  Gms«  Cl 
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DISCUSSION  AND  CONCLUSION 

The  preceding  table  summarizing  the  results  shows  that  the 
higher  the  temperature  at  which  the  wood  pulp  is  bleached,  the 
more  rapid  will  be  the  rate  of  bleaching  and  the  greater  will  be 
the  loss  in  weight  of  the  pulp.  The  rate  of  chlorine  absorbed 
was  the  same  in  each  run  in  spite  of  the  fact  that  the  rate  of 
absorption  of  the  chlorine  and  the  loss  of  pulp  weight  was  dif- 
ferent • 

Insufficient  time  prevented  more  tests  from  being  made  and, 
consequently,  not  enough  data  was  obtained  to  state  exactly  what 
the  optimum  temperature  and  percent  excess  bleach  would  be  for 
a minimum  loss  in  strength  and  shrinkage  of  pulp  on  bleaching. 
Some  work,  however,  was  done  with  varying  consistances,  the 
temperature  and  percent  excess  bleach  remaining  constant.  The 
apparatus  used  was  inadequate  and  the  pulp  mixture  could  not  be 
stirred  sufficiently  at  the  higher  consistancies,  so  the  work 
along  this  direction  was  abandoned  for  the  time  being. 

Strength  tests  were  not  run  on  any  of  the  series  so  nothing 
can  be  definitely  said  about  them  here,  but  it  is  believed  that 
the  strength  decreases  rapidly  as  the  temperature  and  percent 
excess  bleach  are  increased.  However,  the  samples  are  to  be 
sent  to  the  Kimber ly-Clark  Paper  Mills,  Niagara,  Wis.,  to  have 
the  strength  tests  run  on  them  and  the  data  will  be  obtained 
later. 

The  three  factors: 

(1)  The  raw  material. 

(2)  The  process  employed  in  the  manufacture  of  the  pulp. 

(3)  The  purity  of  the  pulp. 


. 


' 


. 

• •: 


. 


. 


. . 


16 


were  not  dealt  with  as  it  would  have  been  impossible  to  effect 
any  control  on  the  second  and  third  factors.  Just  one  kind  of 
pulp  was  used  and  not  enough  time  was  available  to  complete  all 
the  tests  on  this  particular  pulp.  It  would  have  been  very 
interesting  to  compare  the  results  on  “No.  2 Balsam  Dryer"  with 
spruce  and  hemlock. 


. 

. 


17 


SUMMARY 

From  this  investigation  of  the  study  of  bleaching  wood  pulp, 
it  was  found  that  the  higher  the  temperature  and  the  greater  the 
percent  excess  bleach,  the  more  rapid  will  be  the  rate  of  bleach- 
ing and  the  greater  will  be  the  loss  in  weight. 

The  loss  in  weight  varied  all  the  way  for  5%  at  25°C.  to  20.5$ 
at  50°C. 

In  the  rate  of  chlorine  absorption,  the  quantity  of  chlorine 
left  in  the  solutionwhen  the  pulp  had  been  bleached  to  a standard 
color  was  the  same  in  almost  every  test.  It  maintained  almost 
a constant  in  spite  of  a variation  in  the  weight  losses. 

The  amount  of  chlorine  in  grams  per  liter  of  a 12.5$  excess 
and  at  a 2%  consistency,  was  1.22  grams  per  liter.  At  the  end 
of  each  run,  the  amount  of  chlorine  left  was  approximately  .29 
grams  per  liter. 

An  attempt  was  made  to  study  the  effect  of  consistancy 
variation  on  the  bleaching,  but  the  laboratory  teehnique  required 
was  too  involved  so  it  was  temporarily  abandoned. 

The  other  factor,  namely,  percent  excess  bleach,  was  not 
varied.  A 12.5%  excess  was  maintained  throughout  the  investi- 
gation and  the  effect  of  different  percent  excesses  was  not 
studied  due  to  lack  of  time. 


. 

* 

. 

. 


. 


. 


18 


BIBLIOGRAPHY 

(1)  Treadwe 11-Hall,  Vol.  II,  651 

(2)  J.  Soc.  Chem.  Ind.  (1903)  674 

I Chemistry  of  Pulp  and  -Paper  Making.  E.  Sutermeister  (1920) 

II.  The  Manufacture  of  Paper.  R.  V/.  Sindall  (1908) 

III  An  Elementary  Manual  of  Paper  Technology.  R.  W.  Sindall  (1910) 

IV  The  Chemistry  of  Paper  Making.  R.  B.  Griffin  and  A.  D.  Little 
(1894) 

V Chapters  on  Paper  Making.  C.  Beadle  (1907) 

VI  Paper  Making.  A.  F.  Cross  and  E.  J.  Bevan  (1888) 


